The present invention relates generally to laminate webs. More specifically, the present invention relates to a packing laminate web with a protective layer and a method for the manufacture and conversion of such a packing laminate web.
Aseptic packing containers of the non-returnable type used e.g. for sterilized juice or milk are generally made of plastics or plastic-laminated material. The packing material must be sterile or sterilized before it is filled with the desired contents, if packing containers of long keeping quality are to be obtained.
In the manufacture of e.g. milk packages a laminated material in the form of a web is used. The web includes a carrier layer of paper which, on the side facing the contents, is provided with a layer of aluminium foil and an external layer of thermoplastic material. The opposite side of the carrier layer is also covered with a thin layer of thermoplastic. The packing laminate is sterilized immediately before, or during, the conversion to packing containers by being brought into contact with a sterilizing substance, usually hydrogen peroxide, and also by being subjected to heat. After the sterilizing agent has been removed again, the laminate is formed to a tube by folding over and joining in a liquid-tight manner the longitudinal edges of the laminate web. After filling of the tube with the desired contents, the tube is sealed off by transverse seals placed at equal intervals so that individual packing containers filled with sterile contents are produced.
In this and similar methods of manufacture it is also possible to use a presterilized web in rolled-up form. This is supplied in a closed wrapping or a cassette which is inserted into the packing machine, whereupon the laminate web is rolled off and is converted to filled packing containers in the manner described above. In doing this, the whole forming process naturally has to take place in a closed sterile chamber, so as to prevent re-infection of the packing material during the manufacture of the filled packing containers.
This latter method brings with it certain advantages in that it renders unnecessary any use of a sterilizing agent in connection with the forming and filling of the packing containers. On the other hand, the handling of the sterilized packing material is critical, since in order to guarantee sterility, every care must be taken to ensure that from the instant of sterilization right to, and including the final forming of the filled packing containers, the material does not come into contact either with nonsterile objects or with bacteria present in the surrounding atmosphere. This means in practice that after the sterilization every packing laminate has to be kept in a hermetically closed cassette, wherein it can be stored or transported to the packing machine. Moreover, the packing machine must be provided with a sterile chamber including some form of sluice which allows connection of the cassette. Since a very great number of cassettes is required, the method becomes expensive and this, together with the complicated handling procedure, is the reason that aseptic packing machines operate less frequently with presterilized webs, but instead are supplied with non-sterile webs which are sterilized by chemical agents and heat prior to conversion to individual packages.
It is an object of the present invention to provide a packing laminate, web as well as a method for the manufacture and conversion of the same, this method making it possible to avoid the aforementioned disadvantages, and to indicate a simpler technique for the manufacture of sterile packing containers from a packing material web which has been sterilized beforehand.
It is a further object of the present invention to provide a sterile packing laminate intended for the manufacture of sterile packing containers, which is insensitive to surrounding bacteria and which, therefore, can be handled without being enclosed in bacteria proof cassettes or other closed wrappings.
It is a further object of the present invention to provide a method for the manufacture of the sterile packing laminate web, this method being simple and reliable and capable of being carried out without appreciable wastage and also with minimum other costs.
These and other objects of the present invention have been achieved by a packing laminate which is in the form of a primary web, a protective layer being joined to the first side of the web in a detachable but bacteria-proof manner. The packing laminate, before conversion to packing containers, is arranged to be converted to a secondary web, the protective layer being transferred and joined to the other side of the web.
A method for the manufacture of a packing laminate web of this type includes coating the packing laminate on one side by extrusion with a thermoplastic layer forming the protective layer.
A method for the conversion of such a packing laminate web includes delaminating the protective layer from one side of the packing laminate web and transferring it to the other side of the packing laminate web.
Preferred embodiments of the packing laminate web as well as of the method for the manufacture and conversion of the same have been given the characteristics which are evident from the description below.